| 研究実績の概要 |
The investigation of spin orbit effects in exotic materials is of particular importance for developing future spintronic devices. The Weyl semimetal (WS) is a topologically nontrivial phase of matter in which a large spin orbit interaction was theoretically predicted. In this research, we experimentally investigated the spin orbit effect in sputtered WSs, i.e. WTe2 and MoTe2. The films of WTe2 and MoTe2, were fabricated by sputtering for the first time. The structural properties were characterized by x-ray diffraction. A ferromagnetic layer of CoFeB with AlOx capping layer was deposited on the WSs. Furthermore, Hall bar structures were microfabricated for the measurement of spin Hall magnetoresistance (SMR). A SMR ratio of ~0.05% was observed in the sample of WTe2(2 nm)/CoFeB(2.5 nm)/AlOx at room temperature, which is comparable to that in the Pt/YIG system. The temperature and thickness dependence of the SMR was also studied. It is found that the sheet resistances for all the samples with different thicknesses increase with decreasing temperature while the SMR ratio shows an almost constant as the temperature. The spin Hall angle of WTe2 was estimated to be ~-0.04 with a spin diffusion length of 2.5 nm at room temperature for the current conditions. The experimental demonstration of the spin orbit effect in sputtered WSs could contribute the progress of the development of WS-based spintronic devices.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The Weyl semimetals (WSs), i.e. WTe2 and MoTe2, were prepared by a sputtering method. Spin Hall magnetoresistance was investigated in the WS/CoFeB/AlOx heterostructures and the spin Hall angle was achieved. Those experiments were conducted in accordance with our plans. The results are within our expectation. Therefore, the project is progressing smoothly.
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| 今後の研究の推進方策 |
In order to achieve high-quality Weyl semimetals, we plan to use single-crystalline bulk WTe2 or MoTe2 to mechanically exfoliate single or multi layers of the Weyl semimetals. E-beam lithography with lift-off technique will be utilized to pattern the electrodes for transport measurement. The dependence of resistance on magnetic field will be measured by physical properties measurement system (PPMS) in order to characterize the properties of Weyl semimetals. Furthermore, the CoFeB/MgO films will be deposited on the Weyl semimetal layers. Magnetic anisotropy of the heterostructure will be measured by vibrating sample magnetometer (VSM) and magneto-optic Kerr effect. Spin Hall magnetoresistance and spin Hall angles will be investigated and voltage-controlled properties will also be planned to study.
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